Aims in the last few years epidemiological studies in Brazil have detected significant increases in the use and abuse of psychoactive drugs by adolescents: however. there is it paucity of data on the factors associated with this use.Objectives To assess the prevalence of drug use by students from public schools in a Brazilian city and to evaluate the influence of age. school achievement, family, psychosocial, health, demographic and behavioural characteristics on regular drug use.Design This cross-sectional study was conducted using a representative sample of 6417 students attending public schools in the City of Barueri, Brazil and included adolescents from the 5th grade of elementary school to the 3rd year of high school. the Brazilian version of the Drug Use Screening Inventory (DUSI-R) was administered in the classroom by trained educational advisers without teachers being present.Findings prevalence rates for the previous month were: alcohol: 48%, tobacco: 22.5%. cannabis: 14%. inhalants/solvents: 5%, cocaine: 3%, tranquillizers: 0.5%. amphetamines: 0.9%, anabolic steroids: 0.1% and ecstasy: 0.9%. With the exceptions of tranquillizers and amphetamines, the older students reported significantly higher frequencies and amounts of drug use than the younger ones. Boys reported a significantly higher consumption of alcohol. cannabis, cocaine and ecstasy than girls, as well as higher percentages of frequent/heavy use. Logistic regression analysis detected that poor school achievement a poor or bad relationship with those with whom they live. studying in the evening period, presence of antisocial behaviour, family problems and friends who use drugs were factors significantly associated with drug use.Conclusions the findings suggest that preventive programmes should be more comprehensive in scope, rather than focusing only on information about the negative consequences of drug use.